thinking about building a hush enclosure for generator set

[jim rosenthal]

When I bought my NL generator for my 36C, I wanted the sound enclosure (and the dealer had one at a great price!) unfortunately, it just wouldn't fit in the engine room- no way. Even when the Cummins engines were installed, and Tom Slane's crew turned the generator 90 degrees, we STILL couldn't get the NL sound enclosure in there. It is just too big.

The generator's noise isn't unbearable, but it IS there, and it would be nice if it were less. Having a friend go through a new genset installation made me think about trying to build an enclosure that WOULD fit in there.

Has anyone done this, and what was their experience? I am thinking about either fire-resistant FRP panels with a sound-absorbent lining, or aluminum panels etc. A big question is how much heat will build up in there- I realize the set's engine is cooled by the seawater heat exchanger, but what's going to cool the generator end, which will make some heat itself? From what I recall about the NL enclosure, there's some venting for air intake, but I didn't see much else. Is heat buildup not a problem inside generator enclosures?

[SKYCHENEY]

Jim,
A friend of mine has two soft enclosures for his gensets on his 60C. It is basically a metal frame with soft sound insulation hanging over it. I don't know who made it as they were on the boat when he bought it, but it might be worth looking for something like that.

They are quite nice with velcro openings at access points, etc.

[captddis]

Great Southern Insulation in Ft Lauderdale makes the soft enclosures $$$

[DCMY #92]

I built my own soft enclosure. I first installed it on my Onan MDJB. Several years ago I modified it to fit over my current Westerbeke 8kw. The significant change was moving the cooling fan from the front to the top of the enclosure.

The factory enclosures I've seen don't need a separate cooling fan. But I didn't trust the alternator's integral blower to cool the unit alone. I installed a 10" diameter 120VAC fan to move air through the enclosure. Properly placed internal baffles will let the air in and out without the noise.

I used a lead impregnated rubber sheets intended for sound proofing piping supported by a home made aluminum frame. I used pop rivets and screws to fabricate the frame. I used "pull the dot" grommets and studs to attached the rubber sheets. It has held up and worked well now for about 35 years.

During Loose Change's current refit the engine room has been sealed and lined with Soundown. So, I hoping that I don't need the genset enclosure any longer. If so, it'll be available for a new home. I've attached a few rough sketches of my enclosure.

[Fanfare]

Back in the '70s and 80's when I was diving all over the Bahamas we would be weeks on the generator. Under this usage my old 12kw Onan would develop all kinds of leaks in odd places. To better inspect and service it I removed the OEM sound shield. It did get noisier. So I lined the whole generator compartment with Soundown absorbent lead foam in addition to its original Hatteras sound and temperature insulation. This helped, but over thirty or so years the foam is disintegrating and leaving black dust everywhere, and it tends to droop down. One of these days I will remove its remnants. Another round tuit!

I replaced the Onan with a Phasor 12.5kw which I ordered with its sound shield. This has an electric cooling fan from the shield to the compartment. It is large, however, requiring me to entice children and teenagers to gain access to my port generator room side storage and batteries. But now it is really quiet.

I have also added two 120v exhaust blowers and one intake blower to remove the hot air, much of which is from the generator end blowing into the compartment. Only a bit is from the water cooled engine portion. This makes a big difference during the summer and really reduces my air conditioning load. I felt it was important to keep a slight negative pressure in the compartment to remove carbon monoxide.

[jim rosenthal]

This is VERY helpful. I think I can come up with something that will keep the generator end cool and still permit the sound enclosure to absorb the noise and make it all quieter. Thanks to all. Anyone else have suggestions?

[Scottbee]

Has anybody done any work with Dynamat? I used a similar knock-off product on my Onan generator enclosure and it made a substantial difference. Have also used it on the enclosure around my reciprocating air compressor with equally good results.

[bobk]

Jim,

I built an enclosure for a one cylinder Volvo powered generator on my first trawler. It cut the noise nicely. The frame was made of 1" aluminum angle iron. The panels were 1/4" hard wood plywood covered with fire resistant acoustical tile. It had a baffeled air intake and I hard wired a squirl cage blower to cool the electrical part. The blower started and stopped with the generator motor. The enclosure panels were held on with wing nuts on studs. I sold the boat nine years later with no problems associated with the gen or enclosure and it passed the buyers survey with not even a question.

Bobk

[jim rosenthal]

This is pretty much what I had envisioned. Except that I can get high-temp FRP sheeting from McMaster-Carr- and use Dynamat inside it. And a 120vac blower wired to run when the genset is on. I don't think this will cost a huge amount, and I think I can decrease the noise level significantly.

Some of the low-frequency rumble comes up through the boat's structure; an enclosure won't help with that. But if I can cut the noise level by half, it will make an appreciable difference.

[MarioG]

Jim, very important! If your genny is not soft mounted already, do so. Also soft mount the sound shield. Amazing how much "noise" is transmitted through viberation. Don't regret it later...